At Qard.at we used 3 Heroku dynos for: web server, mobile API, and our CMS. We used MongoLab for our MongoDB database. We also used Amazon S3 for static assets like CSS and images. The system was tested with Blitz.io and could scale to 7M hits/month. Our monthly fees were less than $1. The takeaway from this is not that you should run your company on free services, but that you can get started for (as good as) free with a scalable architecture which is then easily transferrable to AWS or similar once the need arises.